091410.doc

9/14/10 Projections, cont? -Distortion -the further away a point is from the standard point, the more the distortion increases -increased scale factor = increased distortion -distortion increases with the size of the area being mapped -not all projections can show the entire area/entire globe -Compromise Projection -all areas have a moderate level of distortion -no areas of high or low distortion -used to make maps of the world (and not much else) -preserve none of the key properties of projections (area, angle, distance) -all characteristics are distorted, but not as severe as in a projection that strives to completely preserve one of the characteristics -Tissot?s Indicatrix -used to evaluate the amount of distortion in a projection -pattern of distortion of the circles helps to indicate distortion on the projection -compromise projections will have evident (but minimal) distortion in all the circles -Figuring out Distance/Direction -Loxodrome/Rhumb Line -line which follows a constant compass heading -useful in figuring out direction from one place to another -not the fasted path from a point to another -Great Circle -covers less distance than loxodrome -line that goes around the Earth that divides Earth into even halves -Equator is the only line of Latitude that is considered a Great Circle -all meridians (longitudes) run along great circles -infinite number of great circle lines on the globe -can find a great circle line between any two points -type of projections can make great circle lines appear longer than straight lines -all planar projections with straight lines drawn from the principal point preserve great circles as straight lines -Interrupted Projections -not a name of a projection, method of showing a particular projection with minimal distortion -introduces lines/tears into the map to help limit distortion -can create illusion of disconnection between places that are actually connected -Maps Characteristics that Affect People -Map Shapes -?odd? looking projections can be used to draw attention -can also make people avoid a map because it looks too ?foreign? and confusing -Focus of Distortion -area distortion can cause people to see areas as more important -Centering -where map is centered causes people to focus on these areas -Curved Lines -people perceive the curved surface of the Earth more readily if lines on the map are curved -may make people more likely to recognize distortion -Characteristics to Determine in making a map -shape of projection -cylindrical, conic, etc. -planar only has a single point of no distortion, cylindrical and conic have entire lines of no distortion -cylindrical projections line of no distortion are equidistant from each other -conic lines of no distortion based on shape of cone -need to chose where lines of no distortion are most appropriate -aspect -shape of area being mapped can influence this -if area is ?long?, N/S aspect may be more appropriate -if area is ?wide?, E/W aspect may be most appropriate -Cartesian Coordinates -translates latitude/longitude coordinates into x,y coordinate system -often used by government agencies -need to know what type of projection was used to make the ?flat? map in order to truly understand the location of something on the Earth